This invention relates to a rotating-anode X-ray tube having a rotating target whose inside is cooled by a flow of cooling fluid, and specifically to a cooling-fluid sealing device for the X-ray tube of this type.
In an X-ray tube, electrons are emitted from a cathode filament and collide against a target to generate X-rays along with a large quantity of heat on the surface of the target. Therefore, a high-power X-ray tube is provided with a rotating target whose inside is cooled by a flow of cooling water to avoid too heating of the target to an extremely high temperature.
Where the cooling water is used to cool the inside of the rotating target, the cooling water have to be sealed not to leak out of the cooling-water passage. A lip seal such as an oil seal and a V-seal has hitherto be used to prevent leakage of the cooling water. The lip seal has a lip made of rubber, silicone or the like. The lip seal comes into contact under pressure with an outer surface of the rotary shaft of the target so as to avoid leakage of the cooling water out of the cooling-water passage which is provided around the rotary shaft.
The lip seal, however, allows the cooling water to leak a bit because a thin oil film has to be formed between the lip and the rotary shaft to assure lubrication of the rotary shaft. Besides, it is difficult for the lip seal to seal entirely the cooling water because (1) the contact between the lip seal and the rotary shaft becomes line contact and (2) the contact pressure between the lip seal and the rotary shaft acts in the radial direction unevenly around the rotary shaft.
The rotating-anode X-ray tube has a cylindrical target which can rotate with a high speed such as of several thousand rpm. Under the high-speed condition, the lip seal is easy to get aged deterioration and the rotary shaft is easy to wear, so that the lip seal can not be used for a long time in a good condition.